The New NY Bridge’s approach span pile caps are installed over groups of steel piles that have been driven deep into the riverbed. The 300-ton platforms are lifted into place by large, barge-mounted cranes.
Constructors use a multi-wheel gantry truck to lift and transport pile cap tubs from the fabrication center to the transportation barges.
The caps—the size of tennis courts—are prefabricated at an offsite facility and resemble concrete tubs with holes at the bottom. Following a thorough inspection, the caps are moved onto barges and transported to the project site.
Once on site, crew members use barge-mounted cranes to position each cap atop a grouping of piles. The cranes are equipped with specially-engineered rigging to securely grip the massive tubs and place them with great precision. Holes at the bottom of the tubs allow the pile tips to slide through. Concrete is then used to seal the tubs to the exterior of the piles.
The project’s reinforced steel is specifically engineered to ensure that it can be precisely formed and positioned. The steel is also coated with a corrosion-resistant layer of zinc through a process called galvanization, which helps protect the steel.
Next, the piles and tubs are fitted with a labyrinth of steel-reinforcing bars, called rebar. The tightly-hewn network of rebar is then enclosed with up to 750 cubic yards of concrete, from the project’s floating batch plants. The resulting composite material, steel-reinforced concrete, combines the strengths of both materials: The concrete can withstand enormous compression, while the steel is capable of taking on great amounts of tension.
The end product: Incredibly strong foundations that will support the new bridge well into the next century.
Learn more about the larger main span pile caps, the project’s geotechnical investigations and the pile welding process.
